Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface, showing our new design.

The broken lines illustrating the display screen and portions of the graphical user interface illustrate portions of the display screen or portions thereof with a graphical user interface which form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 